XtraBackup and Amazon RDS compatibility question

I am hoping someone can give me an answer on this as I have been unable to find it in the documentation.

We have our web servers hosted as Amazon EC2 instances and we are moving our databases into Amazon RDS instances. Part of this move we are wanting to change how the backups are being handled, so were having been looking at XtraBackup as a tool to handle this for us.

From what I have read so far we may not be able to use XtraBackup as it requires access to the database files in a way that having them on the RDS cloud doesn’t allow. I was wondering if someone could clarify if this is true?

Thank you.